Wind turbine wakes are partly responsible for what is commonly referred to as the “underperformance” of wind farms by 10-20% [1-4, 27]. This “underperformance” can be in part attributed to shortcomings in the current power output models to accurately replicate turbine wakes and modulated flow fields throughout a wind farm. Wakes represent an extraction of energy from the free-stream flow that may become inflow for a downstream turbine, depending on the wind direction. Additionally, enhanced turbulence contained within wakes can create increased fatigue loading on downstream turbines [5-7]. Poor understanding of the modulated flows through wind farms leads to uncertainty in optimizing wind farm design and layout [11-12]. As wind farms grow to include more turbines both onshore and offshore, these inter-farm flows and their effects become more complex. As a result, reducing the cost of wind energy through the optimization of wind farm layout and operations demands a full understanding of turbine wake behavior [8-12], including assessing overall wake length and meandering characteristics [12-13, 28] in a variety of atmospheric conditions.
Full-scale observations of the flow through a wind farm are exceedingly limited in quantity and spatial coverage. Supervisory Control and Data Acquisition (SCADA) and individual meteorological tower measurements have provided valuable information related to wind speed deficits within turbine wakes but primarily represent isolated point measurements [1-2, 27] with a course temporal resolution of 10 minutes. Remotely sensed wake observations using scanning LIDAR provide a nearly continuous horizontal flow field, but to date have generally been limited to a maximum range of only a few kilometers while focused only on a single wake [16-18, 33-34]. Typical turbine spacing for existing utility-scale wind farm deployments is 7-10 rotor diameters (D) [3] coinciding with expected typical wake lengths. Although seemingly an extreme case, recent remote sensing observations have traced the length of a single turbine wake beyond 30 D [15].
The need for comprehensive full-scale measurements from within wind farms is well advertised by the wake modeling community to validate and improve current model schemes [1-2, 29-31], including wake behavior in complex terrain [32]. Accordingly, there is a need for a system and method to more accurately evaluate wind flow upstream, downstream and/or within wind farms to provide better optimization of wind farm layouts and operations.